The present invention relates to universal joints for transmitting a moment of rotation in both directions of rotation of relatively rotatable members, such as shafts or the like. The universal joint comprises an outer joint element with an essentially hollow spherical bore surface, an inner joint element with a generally spherical outer surface. One of the surfaces is smooth and the other is provided with a number of generally axially oriented grooves and distributed over its periphery having flanks which open outwardly at an angle and rolling elements arranged between the joint elements engaging in the grooves and guided in pockets of a cage which is also disposed between the confronting surfaces of the joint elements.
The prior art shows joint members generally of this configuration. For example, in German preliminary published application No. 2,219,868, the rolling elements are mounted individually in each pocket of the cage. This arrangement has several disadvantages and drawbacks. For example, production of this joint assembly requires very accurate machining of the grooves in either the outer or inner joint element and a precise finish of the spherical bore surface of these elements so that a slip-free contact of the rolling elements between the outer and inner joint elements is produced and relatively high moments of rotation can be transmitted with certainty. It has been found therefore, that these known joint assemblies are extremely expensive to produce. Additionally, in this known joint assembly, it has been observed that when changing the direction of the moment of rotation, a small rotational clearance exists between the rolling elements, and the groove since the rolling elements move from the inclined flank of one peripheral side of the groove to the opposite inclined flank of the other side of the same groove during a direction change. This rotational clearance may produce running jolts and running noises which are, of course, undesirable.
To this end, in accordance with the present invention, two rolling bodies are provided in a common pocket of the cage and an elastic preloaded means is installed between these rolling bodies which presses the rolling elements reciprocally in a peripheral direction against the flanges of the groove within which they engage. In this manner, a joint assembly for shafts or the like transmitting a moment of rotation in both directions of rotation, is provided wherein there is no rotational clearance when the direction of the moment of rotation is changed and therefore, the assembly is capable of withstanding high moments of rotation. Furthermore, this assembly can be produced rather economically.
With a universal joint assembly in accordance with the present invention wherein two rolling elements are arranged in a common pocket of the cage, one rolling element transmits the moment of rotation acting in one direction and the other transmits the moment of rotation acting in the other direction from the outer joint element to the inner joint element. A rotation clearance free change of direction of the moment of rotation in the joint assembly is provided at the same time since during a change, a displacement of the rolling elements in the grooves of the outer or inner joint element does not take place. Moreover, the joint elements of the assembly are moveable angularly relative to one another, and of course, in turn the axis of the shaft connected to one element is displaced relative to the axis of the shaft connected to the other joint element. During angular displacement in this fashion, the rolling elements roll in their respective grooves and by reason of the particular arrangement of at least a pair of rolling elements in each pocket and the elastic preloaded means, they maintain the desired form fit contact in the groove and the friction fit contact at the spherical bore surface of the outer joint element. In view of this, the confronting surfaces of the joint elements of the assembly, that is, the hollow spherical bore surface of the outer joint element and the spherical outer surface of the inner joint element can be relatively simply and economically produced since they may be manufactured with relatively large diameter tolerances.
Furthermore, the peripheral surface provided with the grooves can also be manufactured economically since the mutual distance of the inclined flanks of each groove do not have to conform to any critical accuracy. This distance may vary within broad limits since the elastically preloaded means between the rolling elements of each row always maintain the rolling elements in a form fit contact with the flanks of the groove which open outwardly at an angle.
The arrangement of the present invention also compensates for different heat expansions between the outer joint element and the inner joint element which occur during operation as a result of different running temperatures of the joint elements. For example, when an increased expansion of the inner joint element occurs, deliterious jamming of the rolling elements between the joint elements does not occur since they can be somewhat displaced in a peripheral direction against the bias of the elastically preloaded means. Similarly, there is no harmful radical clearance between the rolling elements and the joint elements during an increased heat expansion of the outer joint element.
The elastic means may comprise rather simple machine elements such as cup springs or coil springs which are easy to install between the confronting surface of two rolling elements located opposite each other in a peripheral direction and elastically press against the front surfaces thereof.
In accordance with a specific feature of the invention, the elastic means may comprise intermediate elements made of an elastically compressible material, such as plastic, which can be easily and economically produced by conventional injection molding process. Moreover, it is possible to hold the intermediate pieces radially in the bore surface of the outer joint element on the outside surface of the inner joint element and/or at the periphery of the rolling elements partly surrounding them and be guided along the walls of the pocket of the cage. The intermediate pieces may be elastically snapped in place between the rolling elements and in the cage pockets so that the rolling elements are prevented from falling radially out of the cage when the outer joint element is removed or pivoted thereby providing a self-contained unit consisting of rolling elements, intermediate pieces and cage.
In accordance with another feature of the present invention, relatively few grooves are necessary in the bore surface of the outer joint or on the outer surface of the inner joint element and in this manner further simplify the manufacturing process since two rolling elements of each pocket may be arranged in a common groove.
The bore surface of the outer joint is arranged concentrically to the spherical outer surface of the inner joint element so that the depth of the grooves in one of the confronting surfaces may be constant. Of course, grooves with a constant or uniform depth can be machined in the selected surface of the joint element simply and economically.
The cage is of a configuration to conform to the hollow spherical bore surface of the outer joint element and the spherical outer peripheral surface of the inner joint element so that it can rotate and slide on these two surfaces with a form fit. In this manner the rolling elements in the cage are at least partly relieved with respect to absorbing axial forces and consequently are capable of transmitting high moment of rotation forces acting in a peripheral direction without the danger of overloading.